Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $117.83   7.280%   $126.408   $126.41   $126.40   $126.40  
  Purchase #2 $78.28   6.318%   $83.2257   $83.23   $83.25   $83.20  
  Purchase #3 $201.95   13.704%   $229.6252   $229.63   $229.65   $229.60  
  Purchase #4 $118.86   6.772%   $126.9092   $126.91   $126.90   $126.90  
  Purchase #5 $215.74   13.615%   $245.113   $245.11   $245.10   $245.10  
  Purchase #6 $103.61   3.662%   $107.4042   $107.40   $107.40   $107.40  
  Purchase #7 $26.55   3.763%   $27.5491   $27.55   $27.55   $27.50  
  7 purchase totals = $862.82       $946.2344   $946.24   $946.25   $946.10